Mammary adenocarcinoma in a young female hypercholesterolemic rat.

Pathological examination of a 12-week-old female rat with hypercholesterolemia revealed mammary adenocarcinoma. Grossly, one grayish-white nodule was found in the hypoderm near the right posterior mammary gland. Histologically, the nodule was composed of variable-sized epithelial cells which lined the tubules and ducts in one to several layers, accompanied by proliferation of connective tissue in the stroma. Mitotic figures, necrosis and hemorrhage appeared frequently throughout the lesion. The tumor cells had invaded the surrounding muscular tissue.